Comparison of diagnostic accuracy between [18F]FDG PET/MRI and contrast-enhanced MRI in T staging for oral tongue cancer.

ABSTRACT

OBJECTIVE: Integrated PET/MRI with [18F]FDG is advantageous in that it enables simultaneous PET and MR imaging with higher soft-tissue contrast, multiplanar image acquisition, and functional imaging capability without using fat suppression and gadolinium-based contrast agents (GBCAs). The aims of this study were to demonstrate the feasibility of [18F]FDG PET/MRI for assessing the extent of the primary tumor (T) in oral tongue cancer (OTC) based on the 8th edition of American Joint Committee on Cancer (AJCC) cancer staging system, and to compare the diagnostic accuracy between [18F]FDG PET/MRI and contrast-enhanced MRI (ceMRI). METHODS: 18 patients with biopsy-proven operable OTC underwent preoperative regional [18F]FDG PET/MRI and ceMRI within 2 weeks. For [18F]FDG PET/MRI, rainbow-colored PET images were overlaid on the corresponding MR images. Tumor size and the depth of invasion (DOI) were visually measured on [18F]FDG PET/MRI and ceMRI. The size, DOI, and clinical T stage were evaluated using the final surgical pathology as the reference. RESULTS: Of the 18 OTCs, one was not detected by ceMRI due to metal artifacts from an artificial denture, and another due to superficial type (pathological DOI = 0 mm). Tumor sizes measured by ceMRI and [18F]FDG PET/MRI had significant positive correlations with the pathological size (r = 0.80 and r = 0.90, respectively), and DOIs measured by ceMRI and [18F]FDG PET/MRI had significant positive correlations with the pathological DOI (r = 0.74 and r = 0.64, respectively). The means ± SD of size (mm) were 20.4 ± 9.1, 22.9 ± 10.9, and 26.2 ± 10.0, and those of DOI (mm) were 7.1 ± 2.5, 6.9 ± 2.2, and 5.8 ± 3.2 for ceMRI, [18F]FDG PET/MRI, and pathology, respectively. A significant difference was observed in tumor size between ceMRI and pathology (p < 0.05), whereas no significant differences were observed between any other sizes, DOIs, or T stages. The accuracy for T status was 72% (13/18 including 2 undetectable cases) for ceMRI and 89% (16/18) for [18F]FDG PET/MRI. CONCLUSIONS: Although shallow DOIs are often overestimated, regional [18F]FDG PET/MRI without fat suppression and gadolinium enhancement is comparable to and may be substituted for ceMRI in preoperative T staging for OTC patients, reducing metal artifacts and avoiding the adverse effects of GBCAs.